Dodecamethyl-closo-dodecaborate(2-)

Bis(tetraethylammonium) dodecamethyl-closo-dodecaborate(2-), NEt(4)](2)closo-B(12)Me(12)], NEt(4)](2)2, was prepared employing modified Friedel-Crafts reaction conditions from NEt(4)](2)closo-B(12)H(12)], NEt(4)](2)1, trimethylaluminum, and methyl iodide. The NEt(4)](2)2 salt provides sufficient solubility in water to allow the synthesis of the important alkali metal salts A(2)2 (A = Li, Na, K, Rb, Cs) using cation-exchange procedures. The solid state structure of colorless AsPh(4)](2)2 reveals a nearly perfect icosahedral B(12) cluster with B-B bonds ranging from 1.785(3) to 1.807(3) A and B-C bonds of 1.597(3)-1.625(3) A. In contrast, the crystal structure of dark-red Py(2)CH(2)]2 (obtained from NEt(4)](2)2 and Py(2)CH(2)]Br(2)) contains a distorted icosahedral dianion B-B = 1.740(13)-1.811(14) A, B-C = 1.591(13)-1.704(13) A]. In the Py(2)CH(2)]2 salt, the dianion 2(2-) and its dipositive dipyridiniomethane counterion form a red charge-transfer complex. One-electron oxidation of 2(2)(-) by ceric(IV) ammonium nitrate affords the blue, air-stable radical hypercloso-B(12)Me(12)](*-), dodecamethyl-hypercloso-dodecaborate(1-), 2(*-), isolated as the PPN salt. X-ray crystallography reveals that the geometries of the B(12) clusters observed in hypercloso-PPN]2 and closo-AsPh(4)](2)2 are identical and essentially undistorted icosahedra. The anion in the PPN]2 structure contains B-B bonds ranging from 1.784(8) to 1.806(7) A and a range of B-C bonds from 1.596(7) to 1.616(7) A.